First nationwide prevalence study of hip and knee arthroplasty shows 7.2 million Americans living with implants

The orthopedic community and public are well aware that hip and knee replacement operations are among the most commonly performed operations in the U.S. Figures show around 1 million of these procedures are performed each year. But how many people actually are living with a hip or knee replacement in the United States?

This important measure of the impact of joint arthroplasty on public health, known as prevalence, has been missing until the recent release of the Mayo Clinic orthopedics study. Presented in March 2014 at the annual meeting of the American Academy of Orthopaedic Surgeons (AAOS) in New Orleans, the Mayo study is the first of its kind. Its prevalence estimates for 2010 show that:

An estimated 4.7 million Americans have undergone total knee arthroplasty (TKA) and 2.5 million have undergone total hip arthroplasty (THA) and are living with implants. Prevalence is higher in women than in men: 3 million women and 1.7 million men are living with TKA, and 1.4 million women and 1.1 million men are living with THA.

Prevalence increases with age. In adults ages 80 to 89 years, about 6 percent and 10 percent have a history of total hip and knee replacement, respectively.

Prevalence matters

Daniel J. Berry, M.D., of Mayo Clinic in Rochester, Minnesota, and lead Mayo investigator on the team, describes the importance of the groundbreaking prevalence estimates for TKA and THA this way: "These numbers underscore the significant positive impact on health and quality of life that total joint replacement surgeries have made since the era of total joint replacement began in 1969 — the year that Mayo Clinic became the first in the U.S. to perform total hip implant surgery.

"Development of the total knee replacement technique followed in 1971. This large number highlights how these operations have kept a substantial part of our population mobile despite severe arthritis, something that wouldn't have been possible before these technologies were available." For perspective on future planning of health care services, he notes that there are approximately 1.5 times more people living in the U.S. with a knee or hip replacement as there are people living with heart failure.

The study also provides valuable insights into possible future trends in orthopedic care. These include the need to provide specialized health care services for individuals with joint replacements, ranging from chronic care of aging implants to the management of revision surgeries and long-term complications from wear debris or other issues.

Explains Dr. Berry: "Individuals with joint replacement constitute a special population with distinct needs that extend beyond the immediate hospitalization course and the postoperative period." Adds his colleague on the study, Mayo epidemiologist Hilal Maradit Kremers, M.D., "This prevalence study helps start to fill in an important knowledge gap."

Approach: The counting method

Using an approach known as the counting method, the team combined data from multiple databases and applied advanced statistical analytical techniques to produce the prevalence estimates.

In particular, their approach included combining historical incidence data from the National Hospital Discharge Survey and the State Inpatient Databases 1990 to 2010; information from general U.S. Census Bureau population data; and mortality data from the National Center for Health Statistics, and adjusting for relative mortality differences post-procedure for both TKA and THA.

"Having these estimates is a big step forward in planning for the future health care needs of a large and growing patient population," Dr. Berry says. "Joint replacement surgeries have been remarkably successful in improving patients' quality of life, and this prevalence study will help us extend that success into the future."

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